This invention relates to a hydraulic driving device which generates a great driving force at high speed. More particularly, it relates to a hydraulic driving device which is used for the opening and closure of a circuit breaker.
The movable contact of a circuit breaker is engaged with and separated from the stationary contact thereof by a piston which slides within a fixed cylinder. The piston is driven by a hydraulic driving device. In the hydraulic driving device, an oil pressure in an oil chamber of the device changes in response to a command which is externally given to either of two pilot valves in order to turn "on" or "off" the circuit breaker. In correspondence with the oil pressure change, a spool is moved to drive the piston. Such a hydraulic driving device, especially a hydraulic driving device for a high-voltage power breaker, requires to effect the following operations in case of any accident of a transmission system:
(1) Even in case where the command for opening the circuit or the command for closing the circuit is released in a short time in the course of the operation of the hydraulic driving device responsive to the command, the particular operation needs to be continued to complete the opening or closure of the circuit.
(2) In case where the command for opening the circuit and the command for closing the circuit are simultaneously given, or where while the operation of the hydraulic driving device responsive to one of the commands is being conducted the other command is given, the command for opening the circuit must take preference in order to secure the safety of the circuit. This function is called "trip free."
(3) In case where the command for closing the circuit is given in the course of the operation responsive to the command for opening the circuit and where the command for closing the circuit is kept given even after the release of the command for opening the circuit, it is necessary to neglect the particular command for closing the circuit and to hold the circuit in the open state until the next command for closing the circuit is given. This function is termed "anti-pumping."
Japanese Unexamined Published Utility Model Registration Application No. 52-136252 discloses a structure which serves to hold a spool within a main control valve in a position for opening a circuit. The provision of a mechanical device within the main control valve as in the proposal, however, renders the structure of the main control valve complicated and cannot meet the aforecited requirements (1)-(3). In order to operate a hydraulic driving device at high speed in response to the change of commands with a simple structure, it is desirable to utilize the pressure itself of oil flowing in the system of the hydraulic driving device.